The present invention relates to a positive-working radiation-sensitive or photosensitive mixture that contains, as essential constituents, a water-insoluble polymeric binder which is soluble in aqueous-alkaline solutions and a 1,2-quinone diazide and/or a combination of a compound which forms strong acid on exposure to actinic radiation and a compound containing at least one cleavable C--O--C bond. The invention also relates to a radiation-sensitive recording material composed of a layer base on which the radiation-sensitive mixture is deposited.
Positive-working photosensitive mixtures, i.e., mixtures used to produce a copying layer which becomes soluble where exposed, are known and have been described for a wide variety of possible applications, including lithographic plates and photoresists. A substantial number of the properties of these copying layers is determined by the polymeric binder. The binders used for positive copying layers are virtually exclusively phenol formaldehyde or cresol formaldehyde condensation products of the novolak type. For some applications of positive copying layers, however, the properties resulting therefrom are still not ideal. This is true, in particular, of the heat resistance when the mixture is used as a photoresist, and of the number of print runs when the mixture is used as a lithographic plate.
It has been found that substitution of novolaks by binders having higher glass transition temperatures results in a generally better property profile. Thus, a whole series of alkali-soluble binders for positive copying layers have been described, such as, for example, naphthol-based phenolic resins (U.S. Pat. No. 4,551,409), homopolymers and copolymers of vinylphenols (DE 2,322,230, corresponding to U.S. Pat. No. 3,869,292 and DE 3,406,927, corresponding to U.S. Pat. No. 4,678,737), polymers of the esters of acrylic acids with phenols (Japanese Published Specification 76/36,129, Ep 212,440 and EP 212,439) or copolymers of hydroxyphenylmaleimides (Ep 187,517).
Binders of the type mentioned have, however, hitherto not found any practical application. One reason for this is that these polymers do not satisfactorily fulfill an essential requirement imposed on binders of positive copying layers, i.e., the facility for thermal self-crosslinking. This property, which exists in the case of novolaks, is of significance in cases where the copying layer is intended to resist aggressive chemicals. In this respect it is also known to incorporate in the polymers units which, although they are not alkali-soluble, make thermal crosslinking possible (EP 184,044). As a result of this, however, other properties, such as development behavior and storage stability of the mixture, are impaired.
DE 3,820,699 describes polymers based on hydroxybenzylacrylamides which meet the requirement for crosslinkable alkali-soluble monomer units. It is disadvantageous, however, that the polymers can only contain these monomers in a limited amount, since otherwise photosensitivity and development behavior are affected unfavorably.